1. Field of the Invention
The present invention relates to a seek routine of a hard disk drive.
2. Background Information
Hard disk drives contain a plurality of magnetic heads that are coupled to rotating disks. The heads write and read information by magnetizing and sensing the magnetic fields of the disk surfaces. Each head is attached to a flexure arm to create a subassembly commonly referred to as a head gimbal assembly (“HGA”). The HGA's are suspended from an actuator arm. The actuator arm has a voice coil motor that can move the heads across the surfaces of the disks.
Information is typically stored in radial tracks that extend across the surface of each disk. Each track is typically divided into a number of segments or sectors. The voice coil motor and actuator arm can move the heads to different tracks of the disks.
FIG. 1 shows a typical track that has a number of fields associated with each sector. A sector may include an automatic gain control (“AGC”) field 1 that is used to adjust the strength of the read signal, a sync field 2 to establish a timing reference for the circuits of the drive, and ID 3 and Gray Code 4 fields to provide sector and track identification.
Each sector may have also a servo field 5 located adjacent to a data field 6. The servo field 5 contains a plurality of servo bits A, B, C and D that are read and utilized in a servo routine to position the head 7 relative to the track. By way of example, the servo routine may utilize the algorithm of ((A−B)−(C−D)) to create a position error signal (“PES”). The PES is used to create a drive signal for the voice coil motor to position the head on the track.
The servo is written with a servo writer that writes the various servo bits across an essentially blank disk. The disk is sometimes divided into zones. The different zones may produce a dead zone of track addresses as shown in FIG. 2.
The disk drive can enter a seek routine to access data at different disk tracks. During a seek routine a requested address location is provided and a corresponding seek time and drive current are calculated to drive the voice coil motor and move the heads to the desired location. The servo of the disk drive is employed to center the head on the tracks and read the track identifications.
To optimize the servo process most drives utilize a feedforward servo loop. The feedforward loop may include a state estimator that predicts the expected location of the head(s) as it moves across the disk. The state estimator generates and utilizes an estimation error to predict the expected location of the head(s).
The track dead zones can cause a discontinuity in the servo process. FIG. 3 shows a spike in the estimation error at a track boundary. The spike causes unwanted seek acoustics. To account for the track dead zone, the estimation error is set to zero. But such an approach does not account for abrupt changes in the control input signal which leads to increased seek acoustic emission. It would be desirable to provide a servo that more adequately addresses track address discontinuities during a seek routine.